Measuring and indicating circuits



July 9, 1940i v. J. HAwKs MEASURING AND INDICATING CIRCUITS Fild Dec. 31, 1937 hcw Nah I www Patented July 9, 1.940

,UNiTED sTATEs PATENT OFFICE MEAsUaiNG imp mmcA'nNG cmonrrs -Verl J. Hawks, Mountvernon, N.Y., assigner to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application December 31, 1937, serial 10,182,732

6 Claims.

tion point an indication or measure of the relative -time oi' operation of these devices. For example,

such automatic measuring circuits are of utility in a radio or wire telephone system 'employing switching mechanism at the transmitting and receiving stations .to insert complementary types of distortion in the transmitted and received sisnal waves to provide secrecy, in order to give a measure of the amount and direction df asynchronism between lthe operation of the switching apparatus at the two terminals, to facilitate the proper adjustment of that apparatus.

It is an object of the present invention to obtain autotimaticallyV an indication and measure of the relative time of operation of several waveresponsive devices in a system.

This object is attained in accordance with one modification of the invention by a time indicating and measuring circuit in which the operation of the several wave-responsive devices respectively control the charge and discharge of condensers in the control grid circuits of vacuum tubes in such manner that the amount of plate current flow in the plate' circuits of the tubes as indicated by meters therein gives a measurement of the time interval between the operation of the devices and an indication of which has operated first.

Various features and objects of the invention will be understood from the following detailed description thereof when read in connection with the accompanying drawing in which:

Fig. 1 shows schematically a time measuring circuit embodying one modification of the invention; and

Fig. 2 shows diagrammatically a radio signal wave transmission system to which the time measuring -circuit oi the invention may be applied, and the manner of application.

The invention will be described as applied to a radio signalingy system having in addition to the usual transmission apparatus at each terminal station, auxiliary switching apparatus the operation of which requires synchronimtion at the two terminal stations. This switching ap- Il paratus may be mechanisms in a so-called privacy or secrecy system requiring synchronization at the two terminalstations, such as mechanisms for controlling timing cams to shift from one secret vsignal combination to another at a transmitting station and for performing the reverse I operation at a receiving station to reproduce the original signals, as disclosed in the Chesnut et al. Patent No. 1,829,783 or the patent application of A. C. Dickieson Serial No. 149,815, iiled June 23,

1937, which issued as Patent No. 2,132,205, on l0 Oct. 4, 1938.

Referring tothe radio transmission system of Fig. 2, the signal transmitting and the switching apparatus at the transmitting station TSand the signal receiving and the switching apparatus at 18 the receiving station RS are represented by the boxes I and 2 in the signal transmitting circuit TC and in the signal receiving circuit RC at the respective stations, so labeled. The time indicating and measuring circuit of the invention is 20 represented by the dot-dash box 3 at the receiving station RS. The operation of the circuit 3 to measure the directin and amount of asynchronism. between switching apparatus at stations TS and RS requires the transmission of an impulse oi' .control current or tone of suitable frequency f which may be inside or 'outside the transmitted signal frequency band, from the transmitting station TS to the receiving station RS over the intermediate transmission medium lo each time the switching apparatus at lthe station TS is operated. The beginning of a pulse represents the start of operation of the switching apparatus and the length of .the pulse the duration of that operation. This pulse may be transr mitted in any suitable manner. The apparatus at station TS illustrates diagrammatically one method of accomplishing this. l

At the transmitting station TS in Fig. 2, the

cam 4 driven at constant speed by the motor 5 40 may be designed to close the switch 6 to initiate operation of the switching apparatus in the box I at the proper instant and to open the switch 6 at the time desired for the cessation of that operation or for shifting the switching apparatus to contact to connect the source 9 of the control 50 tone ,f to the transmission circuit TC supplying signals to the radio transmission apparatus with-- in the box l. 'I'he deenergization of the winding of relay 1 on the opening of the switch 6 an instant later under control of the cam 4, breaks M from in any suitable manner, for example, by selective circuit I9, and will cause operation of the control device II forming part of the time measuring circuit 3 of the invention, to cause operation of the relay I2 in that circuit for a period determined by the duration of the controlling pulse which in turn will depend on the duration of the switching operation at the transmitting station TS.

At the receiving station RS, a cam I3 of identical design with the cam 4 at the station TS, driven at constant speed by the motor I4, is desired to close and open a switch I5 to initiate and stop operation of the receiving switching apparatus within the box 2 in synchronism with the transmitting switching apparatus within the box at the station TS. Another cam I6 on the same shaft as cam |3 and of identical construction, is driven synchronously with cam I3 by motor I4, and causes the opening and closing of a switch I1 in synchronism with the switch I5 drivenby cam I3. The switch |1'is closed by operation of the cam I6 at the instant the switching apparatus in box 2 operates, to close an energizing circuit from battery I8 for the winding of the synchronizing relay I9 causing the operation of that relay. 'Ihe switch I1 opens at the end of the operation of the switching apparatus to break the energizing circuit for relay I9 from battery I8 and causing that relay to release. The diierence in the time of operation of the two relays I2 and |9.in the time measuring circuit 3 will indicate the amount by which the switching apparatus at station RS is out of synchronism with the switching apparatus at station TS, and the manner in which this time interval is measured by the time measuring circuit 3 of the invention will be explained by reference to Fig. 1 showing in detail that circuit.

'Ihe main elements of the time measuring circuit of the invention in Fig. 1, in addition to the control device II and the relays I2 and |9 illustrated within the box 3 in Fig. 2, are the two pentode vacuum tubes and 2|; the condensers 55 22, 23 adapted to be connected in the control gridcathode circuit of tube 20, and the condensers 24, adapted to be connected in the control grid-cathode circuit of tube 2|; the series resistances 25 and 21 associated with the control grid of tube 20, and the series resistances 28 and 29 associated with the control grid of tube 2|; and the current meters 30, 3| respectively connected in the anode-cathode circuits of tubes 20 and 2|.

'I'he relay I2 is a marginal relay having a biasing winding supplied with biasing current from the battery 32 through a series resistance in such direction that the relay is adapted to be operated quickly on application of energizing current to the operating winding of the relay. The control device I I comprises a single pentode vacuum tube, similar to the tubes 2|! and 2|, the control gridcathode circuit of that tube being connected to the selective circuit l0 in receiving apparatus 2 in the system of Fig. 2 by input transformer 33, and the operating winding of relay l2 is connected in the anode-cathode circuit of the tube I so as to be energized bya iiow of plate current therein, whena tone impulse is impressed upon the control grid-cathode circuit.

Space current is supplied to the plate of the tubes II, 20- and 2| from the common plate battery 34, as indicated. .Heating current is supplied to the heater of the heater type cathode of tube from battery 35, and to the heaters of the heater type cathodes of tubes 20 andA 2| from battery 36. Suitable negative biasing potentials for the control grids' of tubes II, 20 and 2| are obtained from the filament circuit for tubel I, as indicated.

The screen grid of tube is positively biased with respect to the plate and cathode of the tube by a direct connection from the positive terminal of the plate battery 34, and the screen grids of the tubes 20 and 2| are brought to a positive potential less than that of the plates of these tubes by a connection from the positive terminal of plate battery 34 through the resistance 31 and rheostat 38 or 39, as indicated. The rheostats or variable resistances 38 and 39 in the screen grid circuits for tubes 20 and 2| are provided to permit by their adjustment the upper end of the scale of the meters and 3| in the anode-cathode circuits of these tubes to be adjusted to some assigned value (say 10 milliamperes) Since the plate current at any grid voltage for a pentode tube is largely determined by the screen voltage, a cold-cathode tube 40 is connected between the biasing circuit for the screen grids of the tubes 20 and 2| and a common point in the cathode circuits for' these tubes to reduce to a small amount the variations in the screen voltages due to variation in the plate battery 34.

'I'he current meters 30 and 3| in the platecathode circuits of the tubes 20 and 2| are connected in a bridge circuit with the fixed resistances 4I, 42, 48 and 49, and the variable resistances or rheostats 43 and 44 as indicated, to provide a means for adjusting the anode-cathode circuits of the tubes 20 and 2| to make the meters 30 and 3| more sensitive to changes in plate'current, and also to minimize to some extent the effects of slight changes in plate current due to plate voltage variations.

In the unoperated condition of the time measuring circuit 'as indicated in Fig. 1 with no tone being received and With the energizing circuit for relay |9 broken at switch |1, the relays `I2 and I9 are released, and their armatures are held on the back contacts of the respective relays. This connects the control grids of tubes 20 and 2| together through the two 180,000-ohm resistances 21 and 29 and the two 5-megohm resist-v ances 26 and 28 in series. To condition the time measuring circuit to measure the time difference between the operation of the two relays |2 andV I9, the key 45 must be thrown to the left (MEAS) position to remove the normal short circuits across the condensers 22 and 24 in the control grid-cathode circuits of the tubes 20 and 2 I. The key 49 is provided for connecting the additional condensers 23 and 25 of suitable values in parallel with condensers 22 and 24, respectively, to increase the charging capacity by the necessary amount, if the time interval to be measured is greater than a certain value.

The potentiometer 46, the (CAL) jack 41 and the voltmeter 48 associated with the center (ADJ 0) position of the switch 45 are provided for making a .zero adjustment of the meters 30 and 3|, and to permit a calibration (plate current versus time) to be made of the time measuring circuit without involving the use of auxiliary time measuring equipment.

The various steps in adjusting, calibrating and using the time-measuring circuit of Fig. 1 may be described briefly as follows: i

(l) The rheostats 4I and 44 in the bridge circuit in the output of tubes 20 and 2| are adjusted for zero current -in the meters l0 and Il;

(2) The key 45 is thrownto the (ADJ 10).

position, and the rheostats 38 and 39 in the screen grid circuits of tubes 20 and 2l are adjusted to Awhere R is the value of resistance 21 or 28 (180,000 ohms), C is the capacity of condenser 22 or 24 (1' MF), and E is the voltage measured by voltmeter 48 in (4) (Itis better to plot both the calibration characteristic obtained in (4) 4 and the computed time characteristic in terms f of steps of adjustment of the variable'calibrating resistance 46 sincethis automatically takes care of the differences in the normal bias voltage due to ballast lamp, tube and applied voltage variations in the circuit);

(6) Check the zero adjustment on meters 30 and 2|;

(7) Have tone f sent from the transmitting terminal TS for synchronization purposes;

(8) With the synchronizing relay Il deenergized, as indicated by the dark condition of the (TIME) lamp il controlled thereby, the key 45 should be thrown to the (MEAS) position;

(9) Note readings on meter 3l or 2|, after relays I2 and I9 operate, and before lamp IlV goes out, and return key 45 to normal; and

(10) Read time on calibration chart corresponding to the meter reading.

The detailed operation of the time measuring circuit of Fig. l is as follows:

For the case where the switching apparatus at the two terminal stations are out of synchrovnism and the operation at the receivingstatio'n RS..-is behind that at the transmitting station TS, the tone impulse f from the station TS impressed on the input of control tube II by transformer 33 will cause operation bf that tube to operatively energize relay I2 while relay I9 is still In the deenergized condition. Relay I2 as biased is a fast relay and is capable of following the operation of the relays in the switching circuit at the distant terminal quite closely (say, within 0.005 second). Relay I2 will operate to shift its yarmature from the back to the front contact breaking the connection of the control grids of the tubes 20 and 2| through the resistances 26, 21, 28 and 29 and the back contacts of the two relays I9 and I2, and causing the condenser 24 to begin to be charged from battery 35 through the closed contacts of the two relays and resistance 2l Vby virtue of ground being connected toyresistance 29 and a potential of approximately volts which is normally connected to one side of condenser 24. The normal short circuits around condenser 24 and condenser 22 had previously been removed by throwing the key 45 to the left (MEAS) position.

The chargingof condenser 24 will gradually make the voltage on the control grid of the tube 2l less and less negative and result in a corresponding increase in the plate current of tube 2| which will be indicated by the reading of -the meter 3| in its plate circuit. v

When the relay I9 operates in response to the later operation of the switching apparatus 2 at station RS, to shift its armature from the back to the front contact, the connection of ground to resistance 29 through the `former contact is removed and the charging of the condenser 24 is stopped. 'Ihe operation of the relay I9 is indicated to the observer by the lighting up of lamp A Il and its release by the lamp 50 going out.

The reading of the meter 3l must be taken during the known time interval of the pulse received from station TS, that is, before relay I2 releases, and before the synchronizingrelay I9 releases, that is,.while the lamp l0 is stilllighted. 'I'his reading of meter 3| will be proportional to the maximum charge on the condenser 24 and will give a measure of time interval between the operation of the relays I2 and I9, which is the time interval by which the switching mechanism at the two stations are out of rsynchrcnism, when reduced to time unitsby reference to the calibration chart of the time meas- -uring circuit. Of course, this time interval may be returned tothe normal condition indicated. in Fig.1, in which the normal short circuits are placed across the condensers 24 and 22 so that a zero adjustment of the circuit may be made. The key may then be again thrown to the (MEAS) position so that the circuit will be in condition for measuring the asynchronism for a succeeding switching operation when another synchronizing pulse is transmitted from the transmitting station TS in the manner previously described.

In case the switching mechanism at station RS is ahead of that at station TS, relay Il will be operated first by the first switching mechanism which will be indicated by the lighting of lamp 50. The shifting of the right-hand armature of relay Il from the back to the front contact will break the normal connection of the control grids of tubes 20 and 2l to each other through the former contact, and will cause condenser 22 to begin to be charged from battery 35 through the closed contacts of relays I! and I2 and resistance 21 by virtue oi' ground being connected to resistance 21 and a potential of approximately -15 volts to one side of condenser 22. The charging of condenser 22 will makev the voltage on the control grid of tube 20 less and less negative and proportionately increases the plate current in the plate circuit of tube 20, which is measured by meter 30. When relay I2 operates at a later instant in response to the pulse of control energy of frequency f transmitted from station TS under control of the switching mechanism at that station, to break its armature and front contact the ground connection to resistance 21 is broken and the charging of condenser 22 is stopped. The maximum reading of meter 30 during the switch- I9 have released will give a measure of the time interval between the operation of the two 'relays and thus of the amount of asynchronism of the switching apparatus at the transmitting and receiving stations.

In the case where the switching apparatus at 4the two stations are in synchronism and a synchronizing pulse is sent out from the transmitting station TS, the relays I2 and I9 will be operated at the same time and will respectively operate to prevent a charge being placed on the condensers 24 and 22 so that the meters 30 and 3| in the plate circuits of tubes 20 and 2l will not register a reading indicating this synchronism.

It is to be understood that the particular values specified for the elements in the time measuring circuit of the invention as described above and illustrated in the drawing are to be taken by way of example only and not as limiting the invention. Various modications of the circuits illustrated in the drawing and described above which are within the spirit and scope of the invention will occur to persons skilled in the art.

What is claimed is:

l. A circuit for measuring the time interval elapsing between the operation of different switching devices comprising two electron discharge devices, each having an input circuit and an output circuit, a different electrical storage means in the input circuit of each discharge device, means responsive to the operation of each switching device to cause a diierent one of said storage means to be charged at the same uniform rate, means responsive to the operation of the switching device which is last to operate to stop the charging of said one storage means by operation of the other switching device, and metering means in the output circuit of each discharge device for indicating the variation in output current during the time interval in which the storage means in the input circuit of that device is being charged as a measure of that time interval and as an indication of which switching device has operated first.

2. A circuit forv measuring the time interval elapsing between the operation of different switching devices comprising two electromagnetic relays adapted to be operated respectively in response to operation of a different one of said devices, a source of direct current, two electron discharge devices each having a control electrode, a cathode and an anode, and circuits therefor,

' a different electrical storage means in the control grid-cathode circuit of each discharge device, means responsive to the operation of each relay to connect said direct current source across a respectively different one of said storage means so that it will be charged from said source, and responsive to the release of that relay to disconnect said source from the storage means, means also responsive to the operation of each relay to prevent subsequent charging of the other storage means under control of the other relay, and a meter in the cathode-anode circuit of each discharge device for indicating the variation of plate current flow therein during a charging time interval as a measure of that time interval.

ing operation and before the two relays l2 and 3. A system for indicating the amount and direction of asynchronism between the operation of identical switching apparatus at two stations of a transmission system comprising at one station means for causing a pulse of control energy to betransmitted to the other station' each time the switching apparatus at said one station operates, the length of the pulse being proportional to the duration of the controlling switching operation, and at the other station, means for selecting the received control pulses, a first relay operatively responsive to each selected pulsea second relay'operatively responsive to each corresponding operation of the switching apparatus at said other station, two equivalent electrical storage means, means responsive to the operation of said iirst relay to cause one of said storage means to be charged at a uniform rate, and to prevent subsequent charging of the other storage means, means responsive to operation of said second relay to cause said other storage means to be charged at the same uniform rate, and to prevent subsequent charging of said one storage means, and separate means for indicating the charge on each electrical storage means during the charging time interval as a measure of that time interval and as an indication of the station at which the switching apparatus has operated rst.

4. The system of claim 3, in which said indicating means comprising two electron discharge devices each having a control grid circuit including a different one of the electrical storage means, and. a plate circuit including a different current meter for indicating the maximum amplitude of plate current iiowing in the plate circuit during the charging interval.

5. The system of claim 3 in which said indicating means comprises two electron discharge devices each having a control grid circuit and a plate circuit, a different one of said storage means being connected in each control grid circuit so that its charge determines the amount of current iiowing in the plate circuit, a meter in each plate circuit for indicating the current ow thereon, a bridge circuit including the two meters in corresponding arms and means for balancing said bridge circuit to compensate for diierences inthe plate circuit impedances.

6. The system of claim 3, in which said indicating means comprises two equivalent electron discharge tubes each having a control grid, a cathode and an anode, and circuits therefor, a different one of said electrical storage means being connected in the control grid-cathode circuit of each tube so that the charge thereon controls the bias on the control grid and thus the amount of plate current flow in the cathode-anode circuit of the tube, a current meter in the cathode-anode circuit of each tube and means for Calibrating the meters so that the reading of the meter in the cathode-anode circuit of each tube indicates the time required to bring the electrical storage means in the control grid-cathode circuit of that tube to its maximum value during the time the controlling relay is operated.

VERL J. HAWKS. 

